1. Field of the Invention
The present invention relates to an eddy current type multilayered coil for generating an intense AC magnetic field, which generates an intense AC magnetic field used for technological research of magnetic properties, power magnetics, biomagnetics, nuclear fusion and the like, more particularly, which is improved so as to be readily manufactured with an extremely simple structure and to facilitate the use in a low frequency range such as for commercial use.
2. Description of the Prior Art
In general, as for the intense magnetic field generators, the research and the development of such generators is strongly reused to progress by employing large-scale arrangement, which are utilized for the research of material properties in such intense magnetic fields; the development of new manufacturing materials, experiments in nuclear fusion, and the like.
The conventional intense magnetic field generators of this kind can be roughly classified into three groups, that is, destructive intense pulse magnetic field generators such as those of KNER method and implosion method, non-destructive intense pulse magnetic field generators such as those of a multilayered coil type and MIT type, and continuous intense magnetic field generators such as those of a superconductive type and hybrid type.
Those conventional generators are indeed very effective for providing extremely intense magnetic fields. However, those have various defects such that the time duration of intense magnetic fields generated is very short, that special facilities such as extremely low temperature apparatus and large power sources are required and further that only pulse or a DC magnetic field can be provided and hence intense AC magnetic fields cannot be continuously generated. On the other hand, the study of biomagnetics has progressed and the needs for the investigation of the relation between the live body and AC magnetic fields has been increased, and hence there is demand for the development of an intense AC magnetic field generator.
Against the above defects, the inventors have disclosed multilayered eddy current type intense AC magnetic field generators in their U.S. Pat. application Ser. Nos. 160,294 now U.S. Pat. No. 4,857,874 and 160,295 now Pat. No. 4,855,703 (European Patent Application No. EPC88301643.8 and EPC88301644.6) Specifications. In these disclosed intense AC magnetic field generators, according to a novel efficient magnetic flux concentration system in which eddy currents generated in conductors by supplying AC currents through coils are concentrated around holes provided in central portions of those conductors. In order to reduce the leakage of magnetic flux, the hole is provided in the central portion of the circular conductor plate, while cylindrical and annular branches extending in the axial and the radial directions respectively are provided in the peripheral portion thereof. A conductor plate thus formed is further provided with a slit extending from the central hole to the periphery of the plate in a radial direction, and eddy current exciting coils are separately inserted between each of axial and annular branches respectively. In these structures, eddy currents generated in each of the branches by supplying AC currents through each of the inserted coils are concentrated around the central hole, and hence high density AC magnetic fluxes are induced by the concentration of these eddy currents in the central hole, so as to facilitate the continuous generation of an intense AC magnetic field.
However, in these multilayered eddy current type intense AC magnetic field generators, the structure of the eddy current generating conductors is complicated and further, the eddy current inducing coils are formed of conventional wire wound type coils, so that it is difficult to manufacture those generators of a large scale.
Accordingly, the inventors have disclosed an eddy current type multilayered coil for generating intense AC magnetic field in their U.S. Pat. application No. 307,524 now U.S. Pat. No. 4,879,539 (West German patent application No. P3906908.7). As to this coil for generating an AC magnetic field, the structure is extremely simple and hence readily manufactured, the eddy current exciting coil being provided with low impedance, the eddy current generating conductor is thin with a reduced skin effect, and the obtainable magnetic field intensity is extremely higher than the conventional coil of this kind.
In this disclosed eddy current type multilayered coil, the eddy current exciting coil is formed of a spiral conductor plate, between each of the layers of which annular conductor plates are inserted which individually have respective slits extending from central holes to the peripheries of the plates and are insulated therefrom. Such a spiral conductor plate is divided into layers, so as to be readily manufactured with each of the layers insulated from each other by the slitted annular conductor plates and stacked in a cylindrical form, and then spirally connected with each other.
In particular, as shown in FIG. 1, circular conductor plates 1a, 1b, . . . , individually having wide fan-out slits extending from respective central holes to the peripheries of the plates and annular conductor plates 4a, 4b, 4c, . . . , individually having radial slits, are alternately stacked together with annular insulator plates having slits (not shown) being inserted therebetween such that respective slits substantially coincide with each other. The annular conductor plates 4a, 4b, 4c, . . . , in each layer of the stacked conductor plates are connected with each other in order such that, for instance, one end of the annular conductor plate 4a is connected with the other end of the annular conductor plate 4b, so as to form a continuous spiral conductor coil which excites sufficient numbers of eddy current generating circular conductor plates (stacked in a shape of a cylinder 14 as shown by dashed lines) for obtaining an AC magnetic field having a required intensity in a required space. In the example, eddy currents 8, 9, 10, . . . , are generated respectively in circular conductor plates 1a, 1b, . . . , by supplying an AC current 7 through the continuous spiral conductor coil 4a-4b-4c- . . . and hence high density magnetic fluxes are concentrated in a central hole 2.
However, the above previously disclosed eddy current type multilayered coil fo rgenerating AC magnetic field is suited for the use of low voltage and a large current in a comparatively high frequency range because of the structure of the spiral conductor plate coil, and hence it is feared that the range of its application may be restricted to some degree. In this case, a power source such as a transformer for the use of low voltage and large current is required, and hence the function of a wide-frequency-ranged and multi-purposed intense AC magnetic field generator cannot be attained.
The removal of the restriction of the range of use is a problem in the art for the eddy current type multilayered coil of this kind.